From: "J. Bruce Fields" <[email protected]>
A fuzzer recently triggered lockdep warnings about potential sb_writers
deadlocks caused by fh_want_write().
Looks like we aren't careful to pair each fh_want_write() with an
fh_drop_write().
It's not normally a problem since fh_put() will call fh_drop_write() for
us. And was OK for NFSv3 where we'd do one operation that might call
fh_want_write(), and then put the filehandle.
But an NFSv4 protocol fuzzer can do weird things like call unlink twice
in a compound, and then we get into trouble.
I'm a little worried about this approach of just leaving everything to
fh_put(). But I think there are probably a lot of
fh_want_write()/fh_drop_write() imbalances so for now I think we need it
to be more forgiving.
Signed-off-by: J. Bruce Fields <[email protected]>
---
fs/nfsd/vfs.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
index a7e107309f76..db351247892d 100644
--- a/fs/nfsd/vfs.h
+++ b/fs/nfsd/vfs.h
@@ -120,8 +120,11 @@ void nfsd_put_raparams(struct file *file, struct raparms *ra);
static inline int fh_want_write(struct svc_fh *fh)
{
- int ret = mnt_want_write(fh->fh_export->ex_path.mnt);
+ int ret;
+ if (fh->fh_want_write)
+ return 0;
+ ret = mnt_want_write(fh->fh_export->ex_path.mnt);
if (!ret)
fh->fh_want_write = true;
return ret;
--
2.21.0
Ugh, sorry, ignore the two old patches that got sent with the new
series.
--b.
On Wed, May 15, 2019 at 09:20:06PM -0400, J. Bruce Fields wrote:
> From: "J. Bruce Fields" <[email protected]>
>
> A fuzzer recently triggered lockdep warnings about potential sb_writers
> deadlocks caused by fh_want_write().
>
> Looks like we aren't careful to pair each fh_want_write() with an
> fh_drop_write().
>
> It's not normally a problem since fh_put() will call fh_drop_write() for
> us. And was OK for NFSv3 where we'd do one operation that might call
> fh_want_write(), and then put the filehandle.
>
> But an NFSv4 protocol fuzzer can do weird things like call unlink twice
> in a compound, and then we get into trouble.
>
> I'm a little worried about this approach of just leaving everything to
> fh_put(). But I think there are probably a lot of
> fh_want_write()/fh_drop_write() imbalances so for now I think we need it
> to be more forgiving.
>
> Signed-off-by: J. Bruce Fields <[email protected]>
> ---
> fs/nfsd/vfs.h | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
> index a7e107309f76..db351247892d 100644
> --- a/fs/nfsd/vfs.h
> +++ b/fs/nfsd/vfs.h
> @@ -120,8 +120,11 @@ void nfsd_put_raparams(struct file *file, struct raparms *ra);
>
> static inline int fh_want_write(struct svc_fh *fh)
> {
> - int ret = mnt_want_write(fh->fh_export->ex_path.mnt);
> + int ret;
>
> + if (fh->fh_want_write)
> + return 0;
> + ret = mnt_want_write(fh->fh_export->ex_path.mnt);
> if (!ret)
> fh->fh_want_write = true;
> return ret;
> --
> 2.21.0